What batteries to use for off grid power

[Proud Prepper]

When it comes to setting up an off-grid retreat or home, one of the most important decisions you are going to have to deal with is figuring out the right battery system setup for your homestead. Your battery bank is the foundation of your off-grid setup, and it’s something that you are going to have to deal with quite a bit.

If you’re first starting out, the best advice I can give is to bring in a qualified expert who really understands the ins and outs of powering an off-grid home. But if you are dead sent against using outside help, you need to start out slow and start with some cheapo batteries because you are inevitably going to fry them out.

It’s quite common for first-time offgriders to kill their first set of batteries. You’re going to feel a lot better killing off the inexpensive sets than building some massive system and then running it into the ground during the first year.

What kind of Offgrid Batteries are people are using in the real world?

6V Golf Cart Batteries
Because these batteries are so readily available, they are one of the most popular choices for those who are just getting started or watching their budget. While they aren’t the best option for larger setups, they are more than enough for smaller cabins and are a good way to get started.

For an economy system, I recommend 6V golf cart batteries. Just about every manufacturer out there makes T-105 replacements, and they’re all pretty good quality. Most people will get 4-5 years out of these batteries when daily cycled on a small off-grid system.

Pros:

• They take a lot of abuse and are perfect for those who are just getting started.
• They are cheap and easy to find.
• They are relatively light and easy to handle.

Cons:

• They typically only last about five years.
• They are only recommended for smaller setups.

L16 batteries

L16 Batteries were originally designed for commercial use. Their size, deep-cycle performance, and low cost make them an ideal choice for offgriders.

Pros:

• These batteries are suitable for small-to-medium systems.
• They weigh about 100 lbs, so they are relatively easy to move.
• They last slightly longer than Golfcart Batteries and have a lifespan of 5 to 8 years.

Cons:

• They are about two to three times more expensive than golf cart batteries

Deep Cycle Marine Batteries

Deep Cycle Marine Batteries are another easy to find option that many real-world offgriders use to power their homes and cabins. I personally use these for camping, ham radio gear, and as an emergency backup battery bank should things go sideways.

Pros:

• You can find them almost anywhere; most auto part stores, sporting goods stores, and big box stores sell them.
• They are great if you need a cheap emergency backup plan, one where you don’t plan on running these batteries daily for months at a time.

Cons:

• They lose capacity pretty quickly and in most cases will lose about half of their capacity in about 2 1/2 years. These batteries are usually made for casual users who aren’t recharging them on a daily basis.

Long Lasting Dedicated Battery Systems
Once you’re ready to take things to the next level, these are the battery systems that you should start looking at.

Forklift battery systems

Once you are ready to move beyond marine and golf cart batteries, many serious offgriders who need a lot of storage capacity start looking to things like forklift batteries.

Pros:

• These are designed for industrial settings, so they are made to take a beating.
• They are a cost-effective solution and should last much longer than any L-16 battery.
• They have an expected lifespan of up to 15 or 20+ years.

Cons:

• You’re going to need help installing them.
• They weigh anywhere from 1,000 pounds to several thousand pounds.
• Most dealers can tell you everything about forklifts but will have very little knowledge when it comes to using these batteries in an off-grid setup.

TESLA Powerwall 2

The Tesla Powerwall 2 is one of the newest batteries to hit the market and is designed specifically for powering homes. They are compact, stackable and with a built-in inverter, they come ready to integrate with a Tesla solar system. One Powerwall gives you 13.5kWh storage capacity and is warrantied for ten years with unlimited cycles.

Nickel-Iron NiFe Edison Batteries

Edison Batteries are one of the best-forgotten technologies out there. They are a Nickel Iron based battery, which means they don’t corrode like acid-based technology.

PROS:

• This could be the last battery you ever have to buy as they last anywhere from 20-50 years.
• They have a high tolerance to overcharging, over discharging, and short circuiting.
• Freedom from acid fumes.

CONS:

• They are hard to find, and they are one of the most expensive upfront investments on the list.
• They’re not as efficient as lead-based systems.

 

[Silent Earth]

I love useful in depth articles like this. thanks for sharing.

 

[DrHenley]

You might want to mention the different types of lead acid batteries, flooded, sealed flooded, gel and AGM.

I went with AGM, mainly due to the fact that they are safe to charge and use indoors.

 

[Gazrok]

We are likely to go solar, with Tesla batteries. And with a propane tank and generator as well as an added layer for really long cloudy periods. Of course, it will be over the course of the next few years. Currently, we only have a backup generator for some essentials, including a window AC unit in the guestroom, as this will be our occupied room during a long term outage.

I learned all too well during Irma, that I need AC to sleep. But, with that genny, we can power the AC, cycle the mini-fridge, and a decent light if needed.

The solar solution is more to take advantage of some tax breaks, lower the power bill, and just be a little more self sufficient....(and especially to power the water pump and septic, etc.). The propane backup is an extra step (and expense), to be added later than the solar.

 

[lonewolf]

in my case none. I haven't got the storage space for it.

 

[SheilaT.]

I use sealed lead acid golf cart batteries in my little system. They work well enough for me and are still portable enough for me to move around on my own. I'm looking at upgrading to lithium ion though

 

[DrHenley]

I have palletized my main standby system. Total weight a little over 200 pounds This will run everything in the house except the dryer and the central A/C.

Schumacher SC-10030A smart chargers that maintain a constant float voltage of 13.5V
2x VMaxtanks Vmaxslr125 125 aH AGM batteries
PowerBright PW6000-12 6kW (12kW peak) inverter.

My secondary standby system uses
2x DieHard Advanced Gold Group Size Ep-65 75 aH AGM batteries
KISAE SW1220 True Sine Wave 2kW inverter.

I found that a few things didn't like the modified sine wave on the big inverter. Particularly the computers.

The secondary system is not nearly so big and heavy, so I didn't feel the need to palletize it. Besides, for very short term power outages (a common thing here) I only use one battery and only power selected items (like fans and lights)

My tertiary system uses:
EverStart 101 aH deep cycle marine battery (conventional flooded)
PowerBright APS600-12 600 watt inverter

And then when the batteries run down I have a 3500 watt propane genny.

Here is the palletized main system:

 

[Gazrok]

Impressive.

 

[TexasFreedom]

Let me offer another option. Plain lithium ion batteries. You can get 12v, 20 amp-hour Li-ion batteries for $40. That's about $2 per amp-hour.

For comparison, a decent lead acid 12v Trojan-type battery are maybe $150-200. You'll get 120 amp-hours out of them, so you're in the $1 to $1.50 per amp-hour.

The difference is that Li-ion batteries can cycle drained down 80%, maybe 500 cycles. Lead acid batteries really reduce life cycles if you go deeper than 50%. And even at 50%, you're not going to get near the 500 cycle life. And Li-ion are about 1/2 the weight per energy unit.

So let's say you have $1000 to spend on batteries. Say you can get 6 Trojans for that, or about 750 amp-hours at 12 volts. But you can cycle it maybe 30% down on a regular basis, so your 'usable' capacity is about 220 amp-hours.

Spend the same $1000 on Li-ions. Easy math, you get 25 of the 12v 20 a-hr batteries. That's a easy 500 amp-hour capacity. And if you can cycle it 80%, you have a 'usable' 400 amp-hour capacity.

So it has almost twice the usable capacity with maybe twice the life. There are other factors, they don't like extreme cold. And when they fail, they start fires. But they are a viable option.

 

[DrHenley]

Let me offer another option. Plain lithium ion batteries. You can get 12v, 20 amp-hour Li-ion batteries for $40. That's about $2 per amp-hour.

I've been looking for those $40 20 aH Li-ion batteries and can't find them. Closer to $300 ($15/aH).
https://www.amazon.com/Smart-Batter...0087&sr=8-27&keywords=12v+lithium+ion+battery
https://www.amazon.com/12v-20-Lithi...&sr=8-5&keywords=20aH+12v+lithium+ion+battery
https://www.amazon.com/Nexgen-Lithi...&sr=8-6&keywords=20aH+12v+lithium+ion+battery

Also, you need to know the type of aH rating used. Automotive batteries are rated based on a 20 hour discharge (C/20 rating). Marine deep cycle battery aH ratings are for a 1 amp constant discharge rate which doesn't translate to a C/20 rating UNLESS the battery has a 1 amp 20 aH rating. A 100 aH marine deep cycle battery would then be a C/100 rating. A 60 aH marine deep cycle battery would be a C/60 rating, etc.

 

[TexasFreedom]

Doc,

OK, I cheat, I bought them 100 at a time.

But, for the 12v, 20 a-hr Li-ion batteries... ask and you shall receive:
https://www.ebay.com/itm/Portable-D...hash=item2aa6d677c7:m:mwXU-WMlJhvn9ma2o59DCdg

$36 with free shipping and a charger. A warning: most of these ebay type batteries are limited to about 5 amps output. Most larger LiIon batteries have a protection circuit to limit output current (and prevents fires). Depending on what you are running, 5 amps may be sufficient. I cheated again, I had custom batteries made with tested and rated 25 amp output. And I did pay a premium for that. And I have higher quality than you'll find on ebay.

But for many applications, 5 amps is just fine. Or run units in parallel to get whatever amperage you want. Note that most Li-Ion batteries can charge quickly and discharge quickly, usually limited by the protection control circuit.

 

[DrHenley]

OK, that's a whole different ballgame from the kind of batteries I'm talking about. One clue is that instead of being rated in aH, that's rated in maH. Another clue is that the kind of batteries I'm talking about use 0 guage wires. In fact in my case, two sets of 0 gauge wires because one set doesn't carry enough current.

 

[TexasFreedom]

Doc,

If you have a setup drawing that kind of power, consider a change. Many of your smaller inverters (2kW?) run on just 12v DC. That is fine. But if you have a larger inverter, get on with a higher input DC voltage. For example, my big inverter/UPS can generate 70 amps @ 240v AC. But it's input is 16 serial battery cells. So if I am running my water well, for example, let's say it draws 10 amps @ 240v. I only need about 10 amps input (DC voltage). Roughly 1:1 ratio.

So 3 banks of my batteries @ 16 batteries per 'row', and 25 amps per battery, I can run the whole setup. Put them around $3 per a-hr or $60 for a 20 a-hr 12v Li-Ion battery. 48 batteries. $3000 roughly. Almost 1000 amp-hour @ 12v storage, of which 800 a-hrs can be cycled regularly without damage. And no need for super-heavy gauge wiring. And these will last for years and years and years. And if a cell fails, pull that small 4 lb battery & swap it out. Even within each battery, if just one cell fails (they're all 18650 batteries), I can solder it out & replace it.

 

[DrHenley]

I think you are missing the point Texas...which is that what you are calling a 20 amp hour battery is actually a 20000 milliamp hour battery. It's rated in milliamp hours instead of amp hours for a reason, and I can find no information about the C rating.

I am talking about batteries that can deliver over a thousand amps of current. And all I have to do to get higher voltage is just wire them in series. They will still deliver over a thousand amps.

Here is an equivalent Lithium-ion battery (1000 amp peak discharge):
https://www.lithiumion-batteries.co...h4npLqEXcjvEtc3xjZgCK2McFPu6EWYQaAgbvEALw_wcB

 

[TexasFreedom]

Doc,
OK, so a couple of things. First, 1000 milliamps = 1 amp. So 20000 milliamps = 20 amps. And for the batteries I referenced, and I can't say this with 100% certainty, but they likely have a C/4 rating. 20 amp-hour, 5 amp draw limit, so C/4.

In terms of delivering 1000 amps, you are talking about cumulative. And the Li-ion example you give is painful! $1300 for a battery capacity comparable to 1 deep cycle battery? 100 a-hr, 12 v.

Why do you want 1000 amps of output? I understand, if you have a 12 volt inverter, and want 240v-AC output at 50 amps, that means 1000 amps at 12 volts. I've just not seen an inverter rated for 6 or 12 kW that uses only 12v input. I'd be curious the make/model. As I said, my unit is rated for 70 amps @ 240v. But it uses 16 batteries in series. So I never need much over 70 amps from the batteries. It makes not only cabling easier, but also makes the inverter more efficient and less expensive.

And I understand you're not in the market to buy, you have a system. As do I. And neither of us are selling. But others might be looking, I'm just pointing out options.

 

[DrHenley]

No that's actually peak current. You know how car batteries have a cold cranking amps rating? That means they can deliver that current for 30 seconds at 0°F. CCA ratings are in the hundreds of amps for plain car batteries.

 

[DrHenley]

Texas, don't get me wrong...I am not opposed to any promising technology. And I long for the day when lead acid batteries are rendered obsolete.

How many of your "20 ah" batteries do I need to produce 6000 watts of continuous power at 110 volts, and 12,000 watts peak?

 

[TexasFreedom]

No that's actually peak current. You know how car batteries have a cold cranking amps rating? That means they can deliver that current for 30 seconds at 0°F. CCA ratings are in the hundreds of amps for plain car batteries.

I think we're saying the same thing. The battery is not rated for 1000 amps continuous for more than a few seconds. Rather the battery you mentioned is rated for 100 amps continuous.

 

[DrHenley]

The reason peak current is important is that your wiring has to be able to handle peak current, not just continuous. My peak output on the inverter is 12 kW.

 

[TexasFreedom]

Texas, don't get me wrong...I am not opposed to any promising technology. And I long for the day when lead acid batteries are rendered obsolete.
How many of your "20 ah" batteries do I need to produce 6000 watts of continuous power at 110 volts, and 12,000 watts peak?

Sorry, replied without seeing this.

OK, let me do a little math. And address both parts of the question... Part 1:
6000 watts continuous. If this is a common continuous load, I'd want to limit the battery to 10 amps. So 12v x 10a = 120 watts per battery. So that would need 50 batteries (50 x 120 = 6000). Note that I am ignoring inefficiencies, etc. But for 100% discharge, these batteries would run for 2 hours @ 6000 watts and 50 batteries would cost about $3k. To keep under 80% discharge, I wouldn't run it over 1 hour 35 minutes in the real world. Note that total watt-hr capacity is (50 x 20 x 12) = 12000 watt-hours.

Part 2: peak 12kW.
This is easy. Basically it's a short-term load twice the rate. That would mean 20 amps per battery, and I know they can do it for short periods. So the same 50 batteries.

Note that these batteries are maybe 6"x4"x3" (give or take, don't have one in my hand) and weigh about 4 lbs. So this is only about 200 lbs of batteries.

Let me make a comparison. The Trojan 105RE batteries you mentioned. I see they are 6 volt and run $170. For the same 2 hour discharge, it is rated at 146 amp-hour. So that means 73 amps @ 6 volts. That means (6x73) 438 watts. To get to 6000 watts, you'd want 14 of these batteries. That's only $2400, so a bit cheaper. Even though these have about the same watt-hour capacity (14 x 146 x 6, or 12,300 watt-hours), I wouldn't want to discharge the batteries beyond 50%, so I'd only want to run this over 1 hour in this configuration. And note that they are 67 lbs each, so these 14 batteries will weigh an impressive 940 pounds (almost 5 times the Li-Ion batteries!)

But running at C/2 is pretty abusive on that battery. To get a decent battery life, I'd want to back off to the C/10, or 10 hour discharge. Good news is that it has more capacity, 207 a-hr. But that means you only get 20.7 amps of output, or 124 watts. To get to 6000 watts, you need a whopping 49 batteries. $8300. Let's say you discharge it 60%, so it will run for 6 hours.

So there are trade-offs.

The reason peak current is important is that your wiring has to be able to handle peak current, not just continuous. My peak output on the inverter is 12 kW.

Not really. You want your wiring to not heat up with the continuous load. Your surge current could cause a larger voltage drop, but it won't run at that level long enough to worry about heating the wire. No, you don't want the wire to 'smoke' for that short-term current. But if you have wires capable of running 6000 watts continuously, it'll be fine for a short-term 12000 watt load. Heavier wire will mean less losses, so it's not a bad thing to go heavier gauge. But it's not necessary at all.

 

[Mountain trapper]

Before I bought my battery bank I did a lot of research on all the battery types available. Each one has it's pros and cons. So then I consulted with a couple of off grid solar electric engineers and asked their advice. They suggested that I go with flooded lead acid batteries for my system. They are a better choice for my situation where I depend on my system full time.
I optetd for 8 each Crown 6 volt 430 Ah batteries wired for 24 volt. Cost was around $2600.
They do require a little maintenance, but flooded lead acid batteries can tolerate a faster rate of charge/discharge, depth of discharge etc than sealed batteries can, I.e AGM, Gel etc. Flooded lead acid batteries tolerate heat better too.
With periodic maintenance it's possible to get 10 years out of a lead acid battery bank.

 

[DrHenley]

flooded lead acid batteries can tolerate a faster rate of charge/discharge, depth of discharge etc than sealed batteries can, I.e AGM, Gel etc. Flooded lead acid batteries tolerate heat better too.

It is true that non-sealed flooded batteries handle heat better because the electrolyte can be re-hydrated, while with sealed batteries it can't. My understanding is that AGMs have an excess of electrolyte to compensate for some venting at high temperatures, and that eventually if they are run hot they will get low. I suspect this is the cause of failure for AGMs rather than sulfation, which they are much less prone to than flooded.

But with regards to rate of charge/discharge and depth of discharge, AGMs cannot be lumped with other types of sealed batteries:
http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

AGM has very low internal resistance, is capable to deliver high currents on demand and offers a relatively long service life, even when deep cycled. AGM is maintenance free, provides good electrical reliability and is lighter than the flooded lead acid type. While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to sulfation and can sit in storage for longer before a charge becomes necessary. The battery stands up well to low temperatures and has a low self-discharge.
The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life.​

 

[Digout]

The Telephone company I worked for, installed Pure Lead Positive Flooded Lead Acid Cells to run the exchanges/central offices during a power outage. The largest capacity we installed were 2V 3200AHr. Total Voltage was 48V

With regular maintenance they often had a life span of 15 years or more. Naturally they were also pretty expensive, and I can't recall pricing of them.

They were changing to AGM when I left but some brands of AGM had less than a 5 year life. That was expensive.

I inspected one installation of Nickel Iron batteries that needed refurbishment after 50 years service as the 150Kw Diesel starter battery at a TV transmitter site.

Cost was not a huge factor in the total scheme of things in the commercial environment.

 

[TexasFreedom]

One thing that nobody notices with Nickel Iron batteries is their inefficiencies. Don't get me wrong, I drool over their longevity. But when charging/discharging, you lose half your power. And the daily 'drain'.

 

[Digout]

One thing that nobody notices with Nickel Iron batteries is their inefficiencies. Don't get me wrong, I drool over their longevity. But when charging/discharging, you lose half your power. And the daily 'drain'.

Very true

 

[DrHenley]

That's the great thing about lithium-ion and AGM batteries, very low self discharge. Large lithium-ion batteries are getting close to being commercially viable to use as car batteries.

Does anyone know much about lithium iron phosphate batteries? (LiFePO4) They are technically a type of Lithium Ion battery. They seem to be more affordable than the more common Li-ion (LiCoO2) batteries. Supposedly safer, with even lower self-discharge but lower energy density. They seem to be commonly used in motorcycles and jet skis but not automobiles yet.

 

[MNwr786]

One of the biggest (and very often overlooked) off-grid electrical topics is the actual conservation of power. This is NOT a rant about shutting off the lights.

Most of the devices you use on a daily basis (besides the microwave oven) have internal circuitry to convert the outlet 110AC to low voltage DC, typically 12v. Flat screen tv's, laptops, the stereo... Much efficiency is lost by upconverting the 12v batteries to 110v via inverter just to let said device downconvert it right back to 12"ish" volts.

I know with the archetecture of current switchmode supplies that such conversions are fairly efficient, but the 20 or 30 percent adds up!

Its worth grabbing a volt meter and seeing what devices to which you can add a direct 12v power input (and feedback prevention diode).